1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, printer, fax machine, or the like, for forming various kinds of images on sheet-like recording members, and more particularly to a technique for handling a jam which occurs during transport of sheet-like recording members.
2. Description of the Related Art
Image forming apparatuses are well known in the prior art; in such apparatuses, a toner image formed on an image carrier is transferred to a sheet-like recording member by making the toner image electrostatically adhere to it by a transfer carrier, and thereafter the toner image is affixed onto the sheet-like recording member in a fixing section to accomplish the formation of the image. In a certain type of such image forming apparatuses, in particular, a tandem image forming apparatus which comprises a plurality of image forming stations each having an image carrier with various process units arranged around it, a single transfer carrier is formed facing the image carriers in all of the image forming stations, that is, the transfer carrier runs along the entire length of the image forming station array.
As a result, when any one of the sheet-like recording members being transported in succession gets jammed, causing an emergency stop of the image forming apparatus, in many cases the sheet-like recording members remain stopped between the transfer carrier and the image carriers. In particular, if a transport jam occurs in the fixing section, the operation must be stopped immediately. In such cases, it is highly likely that the succeeding sheet-like recording members remain stopped between the transfer carrier and the image carriers.
If a sheet-like recording member stops between the transfer carrier and the image carriers, it is difficult to remove the thus stopped sheet-like recording member by picking it up with fingers, since not only is the sheet-like recording member electrostatically attracted to the transfer carrier, but the transfer carrier is brought into contact with the image carriers. To address this problem, Japanese Unexamined Patent Publication JP-A 62-264144 (1987) and Japanese Unexamined Patent Publication JP-A 7-281534 (1995), for example, propose a paper transport apparatus and a separation failed paper removal apparatus in which, when a jam occurs, the transfer carrier is driven in the reverse direction to the normal paper transport direction and thereby moves the jammed sheet-like recording member back to a position where it can be easily removed.
However, it is difficult to visually locate the sheet-like recording member lying between the transfer carrier and the image carriers; besides, since an image forming apparatus is usually not equipped with means for detecting a sheet-like recording member lying on the transfer carrier, it is difficult for the image forming apparatus itself or the operator to check whether the jammed sheet-like recording member remains attracted to the transfer carrier.
Accordingly, the configuration in which the transfer carrier is driven in the reverse direction whenever a jam occurs has the problem that, if the sheet-like recording member is not on the transfer carrier, the reversing action is of no use and is not only time wasting but also uneconomical. On the other hand, if a detector for detecting a sheet-like recording member on the transfer carrier is to be installed, there arises the problem that the number of components increases, increasing the manufacturing and assembly costs as well as the overall size of the image forming apparatus.
Japanese Unexamined Patent Publication JP-A 5-53405 (1993) proposes an image forming apparatus in which, when a sheet-like recording member gets jammed, only the fixing section is stopped but other sections are operated for a prescribed period of time in order to transport the sheet-like recording member to the position just before the fixing section to facilitate the removal of the jammed sheet-like recording member.
Further, Japanese Unexamined Patent Publication JP-A 11-119490 (1999) proposes an image forming apparatus in which, when a sheet-like recording member gets jammed, the transfer bias applied to the transfer carrier is cut off when transporting the sheet-like recording member to the position just before the fixing section, thereby attempting to reduce the attractive force between the sheet-like recording member and the transfer carrier to a certain degree to facilitate the removal of the jammed sheet-like recording member.
However, the attractive force acting between the transfer carrier and the sheet-like recording member is generated not only by the transfer bias applied to the transfer carrier but also by the attractive force given to the sheet-like recording member by contacting with the charged image carriers.
Accordingly, the force working to attract the sheet-like recording member to the transfer carrier cannot be reduced by merely cutting off the transfer bias as in JP-A 11-119490 cited above, and the attractive force between the transfer carrier and the sheet-like recording member remains high; therefore, there remains the concern that the difficulty in removing the jammed sheet-like recording member cannot be solved with the above arrangement.